Fuel vapor storage and recovery apparatus

ABSTRACT

A fuel vapor storage and recovery apparatus includes a fuel vapor storage canister, said fuel vapor storage canister comprising at least first and second vapor storage compartments filled with an absorbent material, for instance filled with activated carbon, at least a vapor inlet port, an atmospheric vent port and a purge port. Said fuel vapor storage canister defines an air flow path between said vapor inlet port and said atmospheric vent port during shut-off of the internal combustion engine of the vehicle. During purging cycles there is defined an air flow path between said atmospheric vent port and said purge port wherein said first and second vapor storage compartments are arranged in concentric relationship and wherein said first and second vapor storage compartments in flow direction are separated from each other by an air gap diffusion barrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/015,664, filed Dec. 20, 2007, the teachings of which are incorporatedby reference.

FIELD

The present invention relates to a fuel vapor storage and recoveryapparatus for the reduction of evaporative emissions from motorvehicles.

BACKGROUND

Fuel vapor storage and recovery apparatuses including a fuel vaporstorage canister are well known in the art since years. The gasolinefuel used in many internal combustion engines is quite volatile.Evaporative emissions of fuel vapor from a vehicle having an internalcombustion engine occur principally due to venting of fuel tanks of thevehicle. When the vehicle is parked changes in temperature or pressurecause air laden with hydrocarbons escape from the fuel tank. Some of thefuel inevitably evaporates into the air within the tank and thus takesthe form of a vapor. If the air emitted from the fuel tank were allowedto flow untreated into the atmosphere it would inevitably carry with itthis fuel vapor. There are governmental regulations as to how much fuelvapor may be emitted from the fuel system of a vehicle.

Normally, to prevent fuel vapor loss into the atmosphere the fuel tankof a car is vented through a conduit to a canister containing suitablefuel absorbent materials such as activated carbon. High surface areaactivated carbon granules are widely used and temporarily absorb thefuel vapor.

A fuel vapor storage and recovery system including a fuel vapor storagecanister (so-called carbon canister) has to cope with fuel vaporemissions while the vehicle is shut down for an extended period and whenthe vehicle is being refuelled, and vapor laden air is being displacedfrom the fuel tank (refuelling emissions).

In fuel recovery systems for the European market normally refuellingemissions do not play an important role since these refuelling emissionsare generally not discharged through the carbon canister. However, inintegrated fuel vapor storage and recovery systems for the NorthAmerican market also these refuelling emissions are discharged throughthe carbon canister.

Due to the nature of the absorbent within the carbon canister it isclear that the carbon canister has a restricted filling capacity. It isgenerally desirable to have a carbon canister with a high carbon workingcapacity, however, it is also desirable to have a carbon canister with arelatively low volume for design purposes. In order to guarantee alwayssufficient carbon working capacity of the carbon canister typicallyunder operation of the internal combustion engine a certain negativepressure is applied to the interior of the canister from an intakesystem of the engine through a fuel vapor outlet port of the carboncanister. With this atmospheric air is let into the canister to theatmospheric air inlet port to pick up the trapped fuel vapors and carrythe same to an intake manifold of the intake system of the enginethrough the fuel vapor outlet port. During this canister purging modethe fuel vapors stored within the carbon canister are burnt in theinternal combustion engine.

Although modern fuel vapor storage and recovery systems are quiteeffective there is still a residual emission of hydrocarbons let intothe atmosphere. These so-called “bleed emissions” (diurnal breathingloss/DBL) are driven by diffusion in particular when there are highhydrocarbon concentration gradients between the atmospheric vent port ofthe carbon canister and the absorbent. Bleed emissions can be remarkablyreduced when it is possible to reduce the hydrocarbon concentrationgradient. It is quite clear that this can be achieved by increasing theworking capacity of the carbon canister.

However, it should also be clear that only a certain percentage of thehydrocarbons stored in the carbon canister can effectively be purged ordischarged during the purging mode. This can be an issue for cars whereonly a limited time for purging is available, for instance in electrohybrid cars where the operation mode of the internal combustion engineis relatively short.

Another issue arises with the use of so-called flexi fuels whichcomprise a considerable amount of ethanol. Ethanol is a highly volatilefuel which has a comparatively high vapor pressure. For instance, theso-called E10 fuel (10% ethanol) has the highest vapor generationcurrently in the market. That means that the fuel vapor uptake of thecarbon canister from the fuel tank is extremely high. On the other hand,during normal purging modes of a conventional carbon canister only acertain percentage of the fuel vapor uptake may be discharged. As aresult the fuel vapor capacity of an ordinary carbon canister isexhausted relatively fast. The bleed emissions of a fully loaded carboncanister normally then increase to an extent which is beyond theemission values given by law.

In order to improve the purge removal rate during the purging mode fewvapor storage and recovery devices have been proposed which useso-called purge heaters. By heating the atmospheric air which is ledinto the canister through the atmospheric air inlet port the efficiencyof removing the hydrocarbons trapped in the micropores of the absorbentis enhanced remarkably.

For instance, U.S. Pat. No. 6,230,693 B1 discloses an evaporativeemission control system for reducing the amount of fuel vapor emittedfrom a vehicle by providing an auxiliary canister which operates with astorage canister of the evaporative emission control system. The storagecanister contains a first sorbent material and has a vent port incommunication therewith. The auxiliary canister comprises an enclosure,first and second passages, a heater and a connector. Inside theenclosure a second sorbent material is in total contact with the heater.During a regenerative phase of operation of the control system theheater can be used to heat the second sorbent material and the passingpurge air. This enables the second and first sorbent material to morereadily release the fuel vapor they absorbed during the previous storagephase of operation so that they can be burnt during combustion.

Moreover, the storage canister of the evaporative emission controlsystem according to U.S. Pat. No. 6,230,693 comprises two fuel vaporstorage compartments side by side connected by a flow passage. Inparticular the partitioning of the canister actually means a flowrestriction. Because the driving pressure of the flow through thecanister is very low it is an important design consideration that flowrestrictions be kept to a minimum.

SUMMARY

It is an object of the present invention to provide a fuel vapor storageand recovery apparatus including a fuel vapor storage canister which isfurther improved with regard to the so-called bleed emissions, i.e.which has an improved diurnal breath loss efficiency. It is yet anotherobject to provide a fuel vapor storage and recovery apparatus includinga fuel vapor storage canister which has a relatively compact design andlow carbon volume, nevertheless having a high working capacity.

These and other objects are achieved by a fuel vapor storage andrecovery apparatus including a fuel vapor storage canister, said fuelvapor canister comprising at least first and second vapor storagecompartments comprising an absorbent material, at least a vapor inletport, an atmospheric vent port and a purge port, the fuel vapor storagecanister defining an air flow path between said vapor inlet port andsaid atmospheric vent port and between said atmospheric vent port andsaid purge port, wherein said first and second vapor storagecompartments in flow direction are separated from each other by an airgap diffusion barrier.

In particular by providing an air gap insulation between several vaporstorage compartments or several vapor storage beds the hydrocarbondiffusion towards a lower concentration of hydrocarbons, i.e. towardsthe atmosphere, is significantly slowed down, thus significantlyreducing the diurnal breathing losses.

In one embodiment of the fuel vapor storage device according to theinvention at least said first and second vapor storage compartments arearranged in concentric relationship.

The term “concentric” in the sense of the present application does notnecessarily mean that the fuel vapor storage compartments have acircular cross-section. These compartments may also have a rectangularcross-section. In one embodiment of the invention the fuel vapor storagedevice may comprise at least some vapor storage compartments which arearranged side by side.

The fuel vapor storage device according to a preferred embodiment of theinvention is characterized by a third vapor storage compartment arrangedin concentric relationship to said first and second vapor storagecompartments. Said third vapor storage compartment may comprise porousmonolithic carbon as absorbent. For a person skilled in the art it willbe readily apparent that the third vapor storage compartment as well asthe first and second vapor storage compartments, may be filled or packedwith granular activated coal.

In a preferred embodiment of the fuel vapor storage device according tothe invention the vapor storage compartments are integrated in a commoncanister housing, thus fulfilling the need for a compact design havinglittle space requirements.

Each vapor storage compartment may have a circular cross-sectional area,the cross-sectional area of the downstream compartment, whiled regardingan air flow from the atmospheric vent port towards the purge port, beingpreferably larger than the cross-sectional area of the upstream vaporstorage compartment, in order to eliminate dead zones in the vaporstorage beds. Due to this design of the vapor storage compartments thepurging gas may effectively flow through the entire carbon bed, thusimproving the purge removal rate during the purge mode which also leadsto a significant reduction of bleed emissions.

In this respect it is advantageous when the cross-sectional area of eachvapor storage compartment at its downstream end, while regarding an airflow from the atmospheric vent port towards the purge port, is larger orequal to its cross-sectional area at its upstream end.

In one embodiment of the fuel vapor storage device according to theinvention at least one flow diverter is provided, the flow diverterdefining an extended air gap diffusion barrier. Due to the presence ofsuch flow diverter the length of the air path of the diffusion barrieris multiplied, i.e. at least doubled.

The flow diverter may be in the form of a cup-shaped insert at leastpartially surrounding one vapor storage bed within one vapor storagecompartment.

In one embodiment the fuel vapor storage device according to theinvention comprises a purge heater which is activated during purgingwhich leads to a significant improvement of the purge removal rateduring operation of the internal combustion engine.

The purge heater may be located in the purge heater compartment directlycommunicating with said purge port.

It should be appreciated that advantageously the purge heatercompartment is located at the upstream end of the airflow during thepurging cycle, however, alternatively the purge heater compartment maybe located in any one of the fuel storage beds.

In order to enhance the heat transfer from the purge heater into thecarbon bed it is advantageous when the purge heater compartment is atleast concentrically surrounded by a vapor storage bed in anon-insulated fashion, thus allowing heat radiation into the surroundingvapor storage bed. As is mentioned in the very beginning of the presentapplication a higher temperature enables complete purging ofhydrocarbons from the carbon bed and thus increases the capacity of thevolume to prevent fuel vapor breakthrough during a fuel vapor storagecycle. In this context it should be mentioned that an equal temperaturedistribution through the carbon bed improves the purging resultsremarkably.

By “non-insulated” is meant that the purge heater or purge heaterelements are not in direct contact with the carbon bed, however, thepurge heater is not shielded against the surrounding carbon bed. Thepurge heater compartment can, for instance, comprise a cage-likestructure allowing heat radiation into the surrounding carbon bed.

The purge heater may comprise one or more electric heating elementswhich are connected to the source of electric energy, such as forinstance the battery of the car.

The purge heater may, for instance, comprise electrically conductiveceramic as heating elements.

Alternatively, the purge heater may comprise electrically conductivecarbon, preferably porous monolithic carbon. Such porous monolithiccarbon is, for instance, disclosed in US 2007-0056954 A1. Thesemonolithic carbon heating elements have a channel structure allowing airflow through the heating elements and thus allowing an enhanced heattransfer directly through the purging air sucked from the atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will hereinafter be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 shows a cross-sectional view through a carbon canister accordingto the invention and

FIG. 2 shows an exploded diagrammatic view of the compartments of thecarbon canister.

DETAILED DESCRIPTION

A fuel vapor storage and recovery apparatus 1 is illustrated in FIG. 1.The illustration is schematic and the components are not drawn to scale.

The fuel vapor storage and recovery apparatus 1 comprises a vapor inletport 3 connected to a fuel tank (not shown), a vent port 4 communicatingwith the atmosphere and a purge port 5 connected to an internalcombustion engine of a motor vehicle (also not shown). The carboncanister 2 is packed with an adsorbent in the form of granulatedactivated carbon.

During shut-off the engine of the motor vehicle the carbon canister 2 isconnected via vapor inlet port 3 to the fuel tank of the motor vehicleand via vent port 4 to the atmosphere.

As explained in the very beginning of this application, during shut-offof the car the fuel within the fuel tank evaporates into the air spaceabove the maximum filling level of the fuel tank. This vapor laden airflows via vapor inlet port 3 into the carbon canister 2. Duringrefueling of the car, where normally the internal combustion engine isalso shut off, in integrated systems the fuel being pumped into the fueltank causes an air flow through the vapor inlet port 3 the flow rate ofwhich corresponds to the flow rate of refueling. Accordingly,hydrocarbon laden air is pumped with a flow rate of up to 60 l/min intothe carbon bed of the carbon canister. The activated carbons within thecarbon canister absorb the hydrocarbons, hydrocarbon molecules beingtrapped within the internal pore structure of the carbon. More or lesscleaned air will be discharged from the vent port 4.

During engine running cycles of the car a flow path between the ventport 4 and the purge port 5 will be established. The internal combustionengine sucks a certain amount of air to be burnt within the cylinders ofthe internal combustion engine from the atmosphere via vent port 4through the carbon canister 2 into the purge port 5, thereby purging theabsorbent of the carbon canister 2.

In the drawings arrows 6 indicate the air flow during purging of thecarbon canister. The terms “downstream” and “upstream” hereinafteralways refer to the airflow during purging of the carbon canister 2.

The carbon canister 2 comprises first 7, second 8 and third 9 vaporstorage compartments. The first vapor storage compartment 7 is withregard to the airflow during upload of hydrocarbons to the carboncanister 2 the vapor storage compartment next to the vapor inlet port 3and is also the biggest vapor storage compartment.

It will be readily apparent from FIG. 1 that the vapor storagecompartment 7, 8, 9 have a circular cross-sectional area and arearranged in concentric relationship to each other. The first vaporstorage compartment 7 surrounds the vapor storage compartments 8 and 9.Next to the vent port 4 at the upstream side of the third vapor storagecompartment 9 there is arranged a purge heater compartment 10 which hasalso a cylindrical shape, i.e. a circular cross-section. The purgeheater compartment 10 encloses four electric heating elements 11 whichare electrically connected in series with a source of electric energy,for instance through the battery of the vehicle. It is to be understoodthat any electric heating element is suitable for this purpose. Theheating element could for instance be a PTC thirmistor, an NTCthirmistor or for example an electrically conductive carbon heatingelement.

The heating elements may be of cylindrical shape and comprise anelectrically conductive porous carbon monolith, such as for instance, asynthetic carbon monolith generally disclosed in US 2007-0056954 A1.Each heating element 11 provides continuous longitudinal channels (notshown) allowing an airflow in longitudinal direction through eachheating element. The heating elements 11 are only activated during thepurging operation of the fuel vapor storage and recovery apparatus 1.

The purge heater compartment 10 has at its upstream face two inletopenings 12 allowing atmospheric air to be drawn into the purge heatercompartment 10. The purge heater compartment 10 has a relativelythin-walled surrounding wall 13 which is designed such that heatradiation from the resistive heating element 11 may be transferred intothe surrounding carbon bed of the first vapor storage compartment 7.

However, in the first place the heating elements 11 directly transferheat to the atmospheric air drawn into the purge heater compartment 10.At its downstream end the purge heater compartment 11 is in alignmentwith the third vapor storage compartment 9, whereas the third vaporstorage compartment 9 is at its downstream end in alignment with thesecond vapor storage compartment 8, the purge heater compartment 11 andthe third and second vapor storage compartments 9 and 8 beingconcentrically surrounded by the first vapor storage compartment 7.

It should be noted that first and second vapor storage compartments 7and 8 are packed or stuffed with activated carbon in granular form,whereas the third vapor storage compartment 9 may contain a monolithicporous carbon element.

Between the third vapor storage compartment 9 and the second vaporstorage compartment 8, as well as between the second vapor storagecompartment 8 and the first vapor storage compartment 7 first and secondair gaps 14 a and 14 b as diffusion barriers are provided.

The air gap 14 a forming the transition from the third vapor storagecompartment 9 to the second vapor storage compartment 8 is according tothe differences in diameter of the third vapor storage compartment 9 andthe second vapor storage compartment 8 funnel shaped. The first vaporstorage compartment 3 has over its entire length a constant diameterwhich is smaller than the diameter of the second vapor storagecompartment 8. Also the second vapor storage compartment 8 has over itsentire length a constant diameter.

The carbon bed within the second vapor storage compartment 8 is partlyenclosed and held by a cup-shaped insert 15 which defines a U-turn flowpath for the purging air as is indicated by the arrows in FIG. 1. Due tothis design the air path length amounts to double the length of thesecond vapor storage compartment 8. The insert 15 functions as anairflow diverter for the purging air.

The dimensions of compartments of the carbon canister 2 can best betaken from the exploded view of FIG. 2.

Again, with reference to FIG. 1 it can be seen that between a bottom lid16 of the carbon canister 2 and the insert 15 an insulation element 17is provided.

Moreover, at the downstream end of the air gap 14 a ring shaped channel18 defines the transition into the first vapor storage compartment 7. Inthis ring shaped channel 18 flow openings 19 are provided which aredesigned such that the air flow of purge air is directed readily intothe upstream end of the first vapor storage compartment 7.

During running cycles of the internal combustion engine of the vehiclethe fuel vapor storage and recovery apparatus 1 according to theinvention is set to purge mode. Atmospheric air is drawn from theinternal combustion engine of the vehicle from the vent port 4 via inletopening 12 into the purge heater compartment 10. The heating elements 11are electrically connected to the battery of the vehicle during purging.The air flows through and around the heating elements 11 thereby beingheated up to a temperature below 150° C. At the same time radiation heatemitted by the heating elements 11 heats up the surrounding carbon bedof the first vapor storage compartment 7. Heated air flows through thethird vapor storage compartment 9, the air gap 14 a into the secondvapor storage compartment 8 through a bottom grid 20 at the downstreamend of the carbon bed within vapor storage compartment 8 and is thendiverted into upward direction by the cup-shaped insert 15 in theextended and elongated air gap 14 b. On its way the atmospheric air willbe loaded by the hydrocarbons stored in the carbon beds. This air flow,as indicated by the arrows in FIG. 1 within the extended air gap 14 bmakes a U-turn and at the very end of the air gap 14 b flows into andthrough the carbon bed of the first vapor storage compartment 7 and isfinally drawn through the purge port 5 to a purging line leading to theinternal combustion engine.

During shut-off of the internal combustion engine the fuel vaporemissions entering the carbon canister through the vapor inlet port 3will be directed into the other direction towards the vent port 4, theair gaps 14 a and 14 b thereby providing an effective diffusion barrierand thus reducing effectively the bleed emissions.

REFERENCE NUMBERS

-   1 Fuel vapor storage and recovery apparatus-   2 Carbon canister-   3 Vapor inlet port-   4 Vent port-   5 Purge port-   6 Arrows-   7 First vapor storage compartment-   8 Second vapor storage compartment-   9 Third vapor storage compartment-   10 Purge heater compartment-   11 Heating elements-   12 Inlet openings-   13 Wall-   14 a,b Air gaps-   15 Insert-   16 Bottom lid-   17 Insulation element-   18 Ring-shaped channel-   19 Flow openings-   20 Bottom grid

1. A fuel vapor storage and recovery apparatus including a fuel vaporstorage canister, said fuel vapor storage canister comprising at leastfirst and second vapor storage compartments, filled with an absorbentmaterial to form a vapor storage bed, at least one vapor inlet port, anatmospheric vent port and a purge port, said fuel vapor storage canisterdefining an air flow path between said vapor inlet port and saidatmospheric vent port and between said atmospheric vent port and saidpurge port, wherein said first and second vapor storage compartments inflow direction are separated from each other by an air gap diffusionbarrier.
 2. The fuel vapor storage apparatus according to claim 1,characterized in that at least said first and second vapor storagecompartments are arranged in concentric relationship.
 3. The fuel vaporstorage apparatus according to claim 1, characterized in that the fuelvapor storage canister comprises at least two vapor storage compartmentsarranged side by side.
 4. The fuel vapor storage apparatus according toclaim 1, characterized by a third vapor storage compartment arranged inconcentric relationship to said first and second vapor storagecompartments.
 5. The fuel vapor storage and recovery apparatus accordingto claim 1, characterized in that the third vapor storage compartmentcomprises porous monolithic carbon as an absorbent.
 6. The fuel vaporstorage apparatus according to claim 1, characterized in that the vaporstorage compartments are integrated in a common canister housing.
 7. Thefuel vapor storage apparatus according to claim 1, characterized in thateach vapor storage compartment includes a downstream compartment and anupstream compartment each having a circular cross-sectional area, thecross-sectional area of the downstream compartment, while regarding anair flow from the atmospheric vent port towards the purge port, beinglarger than the cross-sectional area of the upstream vapor storagecompartments.
 8. The fuel vapor storage apparatus according to claim 1,wherein each vapor storage compartment includes a downstream end and anupstream end characterized in that the cross-sectional area of eachvapor storage compartment at its downstream end, while regarding an airflow from the atmospheric vent port towards the purge port, is larger orequal to the cross-sectional area at its upstream end.
 9. The fuel vaporstorage apparatus according to claim 1, characterized by at least oneflow-diverter defining an extended air gap diffusion barrier.
 10. Thefuel vapor storage apparatus according to claim 9, characterized in thatthe flow-diverter is in the form of a cup-shaped insert at leastpartially surrounding one vapor storage bed.
 11. The fuel vapor storageapparatus according to claim 1, characterized in that said apparatusfurther comprises a purge heater which is activated during purging. 12.The fuel vapor storage apparatus according to claim 11, characterized inthat the purge heater is located in a purge heater compartment directlycommunicating with said purge port.
 13. The fuel vapor storage apparatusaccording to claim 11, characterized in that the purge heatercompartment is at least concentrically surrounded by a vapor storage bedin a non-insulated fashion, thus allowing heat radiation into thesurrounding vapor storage bed.
 14. The fuel vapor storage apparatusaccording to claim 11, characterized in that the purge heater comprisesone or more electric heating elements which are connected to a source ofelectric energy.
 15. The fuel vapor storage apparatus according to claim11, characterized in that the purge heater comprises electricallyconductive ceramic as heating elements.
 16. The fuel vapor storageapparatus according to claim 11, characterized in that the purge heatercomprises electrically conductive carbon, preferably porous monolithiccarbon.